a. Field of the Invention
The present invention relates to a method of separating the catalyst from the reaction mixture obtained at the time of manufacturing liquid polyol esters of carboxylic acid by reacting olefin, carbon monoxide and polyhydric alcohol in the presence of a catalyst consisting of a cobalt compound.
B. Description of the Prior Art
Esters of polyhydric alcohols having a wide range of use as lubricants, plasticizers, cosmetic materials, surface active agents, etc. have hitherto been manufactured by effecting reaction between natural fatty acids and polyhydric alcohols. However, the natural fatty acids are biased in respect of the distribution of carbon atoms and the resources of natural fatty acids having 6 to 10 carbon atoms as required for materials for use in lubricants for aircraft or heatresisting plasticizers are quite limited. Under such circumstances, with an increase of uses in these fields, the art of esterification by the use of synthetic fatty acids has come into the limelight from the viewpoint of stable supply thereof.
As the method of manufacturing synthetic fatty acids, there are known the Reppe method and Koch method utilizing olefins as the starting material and also the paraffin oxidation method utilizing paraffin as the starting material, but both methods are attended with the forming of side-chain fatty acids as byproducts. These side-chain fatty acids are remarkably inferior to the straight-chain fatty acids in reactivity, so that they necessitate a considerably complicated process for completion of the esterification reaction with polyhydric alcohol, and accordingly, it is difficult to manufacture esters of polyhydric alcohol directly from such fatty acids.
Meanwhile, there have also been made various attempts to synthesize esters directly by the use of olefin constituting the starting material for synthetic fatty acids, carbon monoxide and alcohol with a view to further simplifying the manufacturing method, but these attempts have so far been confined to esterifications with lower monohydric alcohols, such as methanol and ethanol, and direct synthesis of industrially useful esters with polyhydric alcohols is unprecedented.
On the other hand, in the case of the method utilizing the so-called oxo reaction wherein an aldehyde is manufactured by making olefin, carbon monoxide and hydrogen react with one another in the presence of a cobalt compound catalyst, said catalyst assumes the form of dicobalt octacarbonyl or cobalt carbonyl hydride or derivative thereof at the end of the reaction, and accordingly, if the reaction product is directly subjected to distillation, said cobalt compound will be fractionated and the resulting product will be colored, or said cobalt compound will decompose within the still column, giving rise to cobalt metal and hampering smooth operation. Therefore, there is used either the process comprising treating said cobalt compound with hydrogen or steam at a high temperature to convert it into cobalt metal and thereafter transforming this cobalt metal to a form usable for the reaction, or the process comprising treating said cobalt compound with an aqueous solution of acetic acid to convert it into cobalt acetate and thereafter transforming this cobalt acetate to a form usable for the reaction. Admitting that both processes are also applicable in the case of making olefin, carbon monoxide and alcohol react with one another, yet they are industrially undesirable on account of the complicated process involved therein.